Three human RNA polymerase III-specific subunits form a subcomplex with a selective function in specific...

Area of Science:

• Molecular Biology
• Gene Transcription
• Protein Biochemistry

Background:

• RNA Polymerase III (Pol III) orchestrates gene transcription through a multi-step process including recruitment, initiation, elongation, and termination.
• Human Pol III is a large complex comprising 16 subunits, with potential modifications observed in HeLa cells.

Purpose of the Study:

• To elucidate the functional role of specific human RNA Pol III subunits in transcription initiation.
• To identify the components responsible for promoter-dependent transcription initiation.

Main Methods:

• Immunopurification of human RNA Pol III.
• Partial denaturing conditions and sucrose gradient sedimentation to isolate subcomplexes.
• cDNA isolation and characterization of RNA Pol III subunits.
• Recombinant protein expression and functional reconstitution assays.
• Co-immunoprecipitation to study protein-protein interactions.

Main Results:

• Human RNA Pol III consists of 16 subunits, with a distinct subcomplex of hRPC32, hRPC39, and hRPC62 identified.
• This subcomplex is crucial for promoter-specific transcription initiation, while the core polymerase lacking it performs non-specific initiation.
• Reconstitution with the hRPC32-hRPC39-hRPC62 subcomplex restored specific initiation capability.
• hRPC39 was shown to interact with hTBP and hTFIIIB90, key components of transcription factor IIIB.

Conclusions:

• The hRPC32-hRPC39-hRPC62 subcomplex is indispensable for the specific recruitment of RNA Pol III to promoter DNA.
• Interactions between hRPC39 and transcription factor IIIB mediate the precise binding of RNA Pol III to the transcription initiation site.